Sheffield born former Labour peer Lord Hattersley has revealed how his Catholic priest father ran away with his mother - two weeks after marrying her to another man.
Lord Hattersley only learnt later in life that his father Frederick was a Catholic priest who met his mother Enid while 'instructing' her into the Catholic Church before she was married to miner John O'Hara in Shirebrook, Nottingham.
The two fell in love and ran away together and married, leading to Mr Hattersely being ex-communicated, the former Labour peer has revealed.
Lord Hattersley, one of the most influential figures in the Labour party until he resigned in 2015, was not even told that his father was once a priest as a child.
Despite his in-depth knowledge of the Catholic Church, he had thought that he served as a civil servant and spent other periods in life unemployed.
But when he died in 1973, he received a letter from the Bishop of Nottingham that alluded to his past, Lord Hattersley writes in his new book.
At the time, his mother told her son - then in his 40s - she met the priest when he placed and order at the local coal merchant's where she worked and they fell in love.
However, he met the bishop as part of his research into a new book based loosely on his father's life story and learned of the true scandal of their relationship.
Lord Hattersley, 84, told The Telegraph: ‘My parents met when he was instructing her to join the Catholic Church, they fell in love and they decided nothing could be done about it. He officiated at the wedding ceremony and they ran away two to three weeks later.
Mr O'Hara died intestate in Mansfield in July 1956. His estate, valued at £373 12s 10d, was left to his ex-wife - who went on to become Lord Mayor of Sheffield - suggesting he never moved on or had children.
Enid and Frederick married a few months later, which led to his ex-communication from the church as Catholic priests are not supposed to get married.
Lord Hattersley had alluded to the scandal in an introduction to his autobiography A Yorkshire Boyhood in 2001 but tells the full story in his new book The Catholics.
In the introduction, he writes: 'My father - parish priest of St Joseph’s church in Shirebrook, Nottingham - had met my mother after he agreed to "instruct" her for admission to the Catholic Church in anticipation of her marriage to a young collier.
'Father Hattersley had performed the wedding ceremony. Two weeks later the priest and the bride ran away together. For the next forty-five years they lived in bliss - married after my mother’s first husband died in 1956.'
The Catholics, following Catholicism in Britain from the Reformation to the present day, is published by Chatto & Windus and available now
Lord Hattersley, who was born in Sheffield in 1932, was a socialist and Labour supporter from his youth, electioneering at the age of 12 for his local MP and city councillors.
He became an MP in 1964 for the Birmingham Sparkbrook constituency and held the seat for the next eight general elections.
He was deputy leader of the Labour Party under Neil Kinnock in the 1980s and early 90s and he stood down at the 1997 General Election before becoming a peer.